1. Field of Invention
The present invention relates to a pump-integrated flexible actuator, such as one that can be used in a pet robot which is generally in contact with human beings, a work robot used to perform agricultural tasks, such as holding pieces of fruit which have irregular shapes and which are likely to be damaged, as well as various other varied uses.
2. Description of Related Art
An actuator that holds objects is known, which is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 5-172118 and 5-164112, in which a cylindrical elastic member that includes a plurality of pressure chambers is provided. The cylindrical elastic member is bent by controlling fluid pressure which acts on each pressure chamber, thereby holding or pressing the object (this art is hereinafter referred to as a xe2x80x9cfirst related artxe2x80x9d).
An actuator that is different from the first related art is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2-17204, in which a driving source and a pump are assembled in a hydraulic cylinder (this art is hereinafter referred to as a xe2x80x9csecond related artxe2x80x9d).
Since the cylindrical elastic member that is included in the actuator according to the first related art is soft, the actuator can softly contact human beings and objects.
However, this actuator must be provided with a pump for supplying work fluid and piping for feeding the work fluid to the pressure chambers that are disposed outside of the cylindrical elastic member. Therefore, there is a problem in that the size of the actuator increases. There is another problem in that the pipes block the movement of joints of a robot when the robot uses this actuator as, for example, an arm. Therefore, it is difficult to use the actuator for a pet robot or the like because the robot must be provided with a number of sensors and complex mechanisms, since delicate movements that are similar to those of a living creature are required of such a pet robot.
The actuator according to the second related art, in which a pump and piping are not exposed to the exterior, cannot softly contact human beings and objects because driving members, such as a piston rod, are hard. It is therefore difficult to use the actuator for a pet robot or an agricultural work robot for holding pieces of fruit and other objects.
Accordingly, it is an object of the present invention to provide a pump-integrated flexible actuator, in which the size of the actuator, which has a simple configuration, is reduced. It is also an object of the invention to provide an actuator that softly contacts human beings when the actuator is used as a pet robot, and that can reliably hold objects when the actuator is used as an agricultural work robot.
The present invention provides a pump-integrated flexible actuator which includes a movable unit provided with a plurality of fluid chambers that have fluid sealed therein, the movable unit being movable with the fluid chambers being deformed by a transfer of the fluid between the fluid chambers; a pump unit integrated with the movable unit, that transfers the fluid between the plurality of fluid chambers; and a pump driver that controls driving of the pump unit. The plurality of fluid chamber that have fluid sealed therein are preferably disposed parallel to each other. According to the invention, an actuator having a simple configuration and a reduced size, in which a movable unit of the actuator is capable of operation, is obtainable.
The movable unit is preferably provided with at least one long and narrow deformable tube that forms the plurality of fluid chambers that have fluid sealed therein, and a flexible core disposed parallel to the tube, that restricts expansion of the tube in a longitudinal direction thereof. The movable unit is preferably provided with at least two long and narrow tubes, which are capable of expansion and contraction, disposed parallel to each other, each tube forming the fluid chamber, and a flexible core disposed between the tubes, that restricts expansion of each tube in a longitudinal direction thereof. According to the invention, the movable unit can be reliably deformed in a manner that is similar to a living creature because the core restricts expansion in a longitudinal direction of each tube and allows expansion in a widthwise direction thereof when the core bends while maintaining the tubes in parallel with each other.
The tube, which is disposed at a side of the movable unit to be brought into contact with an object when a pressing force and a holding force of the movable unit act on the object, is preferably made of a soft and elastic material. According to the invention, the object can be pressed and held without being scratched because the tubes are made of a soft material and contact the object softly in a state in which a plurality of plane-contact portions of action are provided.
When a soft member covers the pump unit, the actuator becomes safer because hard parts are not exposed to the exterior.
The fluid that is sealed in the fluid chambers is preferably a liquid, and an outer cover having a liquid-absorbing function preferably covers the movable unit at the periphery thereof. According to the invention, the liquid does not leak to the exterior because it is absorbed by the outer cover even when the liquid leaks from the movable unit.
The pump-integrated flexible actuator preferably further includes a depressurization mechanism which reduces inner pressure of one of the plurality of fluid chambers by having the plurality of fluid chambers communicate with each other when the inner pressure of the one of the plurality of fluid chambers increases to an abnormal level. According to the invention, when an excessive external force is applied to the movable unit and pressure in one of a plurality of the fluid chambers is thereby increased to an abnormal level, the depressurization mechanism reduces the increased pressure in the fluid chamber, thereby avoiding explosion of the fluid chamber, whereby a fail-safe mechanism against an excessive external force can be provided.
The core is preferably formed with a signal wire or an electrical wire connected between the pump unit and the pump driver. According to the invention, the signal wires and the electrical wires are prevented from becoming damaged, which enables electric shocks and the like to be avoided.
The pump driver is preferably disposed in the movable unit which seals liquid therein so that the pump driver is in contact with the liquid. According to the invention, the pump driver is cooled because heat generated by the pump driver is absorbed by the liquid, and a more compact actuator is obtainable by virtue of the pump driver disposed inside the movable unit.
The pump-integrated flexible actuator preferably further includes a reservoir that stores a predetermined amount of fluid; and a supply member that controls supply of the fluid stored in the reservoir to each fluid chamber of the movable unit. According to the invention, the work fluid in the reservoir is supplied into the fluid chambers by operating the supply member and the inner pressure of the fluid chambers is thereby increased, whereby the movable unit can be made to be rigid. With this arrangement, when the actuator is used as a component for, for example, a pet robot, the actuator can move into a state in which the pet robot is tense other than the state in which the actuator is bent with an operation of the pump unit.
Two pump units are preferably integrated with the movable unit at respective longitudinal ends of the movable unit, and the two pump units preferably simultaneously operate to transfer fluid between the plurality of fluid chambers. According to the invention, the actuator can be moved quickly by increasing the bending speed of the movable unit with the two pump units transferring the fluid between a plurality of the fluid chambers.
Each pump unit is preferably provided with a detachable connecting part, such that when a pair of the movable units are connected to each other in series, the movable unit is connected to the other movable unit at the pump unit of each movable unit. According to the invention, a pair of the flexible actuators can be mounted to and removed from, each other through a one-touch operation, whereby a device, that is capable of an easy dismounting operation with respect to the actuators is obtainable.
The pump unit preferably includes a diaphragm which defines a pump fluid chamber between an end of the movable unit and the pump unit. A piezoelectric element is preferably laminated on the diaphragm. The pump unit is preferably provided with a valve that sets a direction of the transfer of fluid between one tube that forms the fluid chamber and another tube that forms the other fluid chamber via the pump fluid chamber.
According to these inventions, a more compact actuator that is lighter can be provided by virtue of the pump unit reduced in size.
The pump unit preferably includes the same number of unidirectional-flow-type pumps as the number of fluid chambers. Each fluid chamber communicates with one unidirectional-flow-type pump which transfers fluid from the fluid chamber to another fluid chamber and another unidirectional-flow-type pump which transfers the fluid from another fluid chamber to the fluid chamber. According to the invention, an actuator can be provided in which a bidirectional operation, which is performed by using a bidirectional-flow-type pump and a direction-switching valve, is made possible by only using unidirectional-flow-type pumps that have a simple configuration.
The plurality of fluid chambers are preferably each provided with a pressure sensor, and the pump driver preferably computes an actual operational force of the movable unit according to determination by the pressure sensors and controls driving of the pump unit. According to the invention, the pressure sensor detects the fluid in each fluid chamber and the operational force of the movable unit is controlled, so that the movable unit operates with an optimum operational force, according to pressure data, whereby the movable unit can operate at a high accuracy.
The plurality of fluid chambers are preferably each provided with an acoustic wave generator that generates acoustic waves and an acoustic wave sensor that senses the acoustic waves, and the pump driver preferably computes an actual amount of displacement of the movable unit according to a determination by the acoustic wave sensors and controls driving of the pump unit. According to the invention, the movable unit is controlled so as to be moved by an optimum amount of displacement according to a determination by the acoustic wave sensor which determines the propagation time and the phase of the acoustic waves generated in the fluid chambers, whereby the movable unit can operate at a high accuracy.
The pump unit preferably includes a diaphragm which defines a pump fluid chamber. Variation in current generated when a pressure is applied to the diaphragm which is applied with a voltage is preferably inputted to the pump driver. The pump driver preferably computes an actual operational force of the movable unit according to determination of the variation in current that controls driving of the pump unit. The pump unit may include a diaphragm which defines a pump fluid chamber, a plurality of the fluid chambers may each be provided with an acoustic wave sensor that senses acoustic waves generated by the diaphragm, and the pump driver may compute an actual amount of displacement of the movable unit according to a determination by the acoustic wave sensors that control driving of the pump unit.
According to the invention, the operational force and the displacement of the movable unit are controlled by using a diaphragm, whereby a simple control-mechanism can be provided.
The pump driver preferably includes a table that computes an operational force and displacement of the movable unit from the determined acoustic waves and pressure. The propagation time or the phase of the acoustic waves, which the acoustic sensor determines, differs between cases where the movable unit applies the operational force to the exterior and where the movable unit does not apply the operational force to the exterior. Therefore, according to the present invention, the pump driver is provided with a table that computes the operational force and the amount of displacement of the movable unit from the determined acoustic waves and the pressure. With this arrangement, the pump driver can control the movable unit by referring to the table so that the movable unit moves by an optimum displacement amount according to the cases where the movable unit does not apply the operational force and where the movable unit applies the operational force. Therefore, the operational force can be controlled to be constant in any displacement state of the movable unit.
The movable unit preferably includes a light generator and a light receiver that oppose each other, or a light generating/receiving member and a reflector that oppose each other, and an actual operational force of the movable unit is preferably computed in accordance with determination by either the light receiver or the light generating/receiving member so that drive of the pump unit is controlled.
According to the invention, the operational force and the displacement of the movable unit are controlled by using either a light generator and a light receiver or a light generating/receiving member and a reflector, whereby a simple control mechanism can be provided.
The pump driver preferably includes a table that computes an operational force and displacement of the movable unit from an amount of light which is determined by the light receiver or the light generating/receiving member.
According to the invention, the pump driver is provided with a table that computes an operational force and displacement of the movable unit from a determined light amount, whereby the pump driver can control the movable unit so that an optimum displacement of the movable unit is obtainable, by referring to the table, either when the operational force of the movable unit is applied or when the operational force thereof is not applied.